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A detailed high pressure investigation is carried out on $Fe_4Nb_2O_9$ usingangle resolved x-ray diffraction and Raman spectroscopy measurements. We find astructural transition from the ambient trigonal phase to a monoclinic phaseabove 8.8 GPa. The structural transition is assumed to be driven by a largedistortion of $Nb-O_6$ octahedra as seen from x-ray diffraction analysis and alarge pressure dependence of $Nb-O_6$ octahedra breathing Raman mode. Anomalousbehaviour of Raman modes and increase in the phonon life time at the phasetransition pressure indicate a trigonal paramagnetic phase to a monoclinicantiferromagnetic state above 8.8 GPa. Decrease in the diffusive scatteringrate of low frequency electronic contribution contradicts the results ofdecrease in intensity of high frequency electronic response and excludes thephenomenon of insulator to metal transition. Instead the enhancement of theintensity of the Raman modes till about 8.8 GPa indicate a large change inferroelectric polarization of the sample indicating pressure induced re-entrantmagentoelectric effect in $Fe_4Nb_2O_9$.

Pressure driven re-entrant magnetoelectric transition in honeycomb $Fe_{4}Nb_{2}O_{9}$